Cutting torches are commonly used for cutting metal by locally heating the metal to its oxygen ignition temperature with a preheat flame fuelled by an oxygen/fuel gas mixture and subsequently cutting the metal with a high velocity cutting oxygen stream supplied through the torch, thereby releasing a considerable amount of thermal energy which further heats the surrounding metal. The high velocity oxygen stream physically removes the molten material by oxidation, thereby cutting the metal.
Cutting torches are generally recognized to be one of the most efficient methods of cutting metal. In industrial processes for cutting slab steel at a casting or rolling mill and the like, cutting torches are often operated continuously. Such torches are occasionally damaged or subject to blowout. Because industrial processes of this type cannot be halted to replace or repair torch equipment, a standby torch is generally kept lit and operating around the clock so that it can be used if the primary torch fails. The continual operation of a standby torch consumes large quantities of cutting gas and compressed oxygen.
In other metal cutting applications using gas fuelled cutting torches, the cutting torch is often used sporadically while material marking, placement, or other arrangements of material or personnel are in progress. Shutting off a cutting torch for short periods of time between cutting jobs is inefficient. Consequently, the cutting torch may consume significant quantities of fuel and compressed oxygen between cuts.
It is therefore desirable to provide a gas flow control assembly for a gas fuelled cutting torch that provides a cutting torch which will operate in a pilot mode wherein a small flame is sustained at a cutting nozzle installed in the torch head when the torch is not in active use, and will instantly shift to a fully-tuned preheat cutting/mode on demand.